In semiconductor wafer processing, for example, CVD, and similar methods, substrates such as silicon wafers are typically heated to various temperatures in order to carry out different thin film deposition or etch operations. Various techniques have been employed in the prior art for heating these thin substrates, including: (1) infrared heating; (2) visible light source heating; (3) radio frequency coupled heaters; and (4) hot plate heaters.
In the first type of heater, the substrate was physically rotated past an array of infrared lamps in an effort to achieve required uniform temperatures throughout the silicon wafer. However, the physical rotation step tended to interfere with distribution of gas flow over and onto the wafer, thus resulting in processing limitations.
In the second heating method, temperature uniformity was attempted by employing very complex and expensive optical reflectors. Stability and uniformity of temperatures were determined by complex radiative interaction of the various surfaces according to their respective emissivities.
The third method, while also complex and expensive, has been commonly employed particularly for processing temperatures in the range of 1,000-1,200 degrees centigrade (.degree.C.). However, this method has offered sub-optimal temperature uniformity on the substrate while being very difficult to manipulate in order to achieve even a moderate level of temperature uniformity.
The fourth method has typically been employed for low temperature applications, for example below 500.degree. C. Such hot plate heaters have commonly consisted of an embedded resistance wire in a ceramic or dielectric plate or a high thermally conductive metal such as aluminum. While satisfactory temperature uniformity has been achieved by this method, it has not been found suitable for use in high temperature processing due, for example, to limits established by metal melting points, bonding materials employed and the emission of contaminants from the heating element and the metals particularly at such higher temperatures.